Remove `Deref` and `DerefMut` implementations previously dereferencing
to the `NetworkBehaviour` on `Swarm`. Instead one can access the
`NetworkBehaviour` via `Swarm::behaviour` and `Swarm::behaviour_mut`.
Methods on `Swarm` can now be accessed directly, e.g. via
`my_swarm.local_peer_id()`.
Reasoning: Accessing the `NetworkBehaviour` of a `Swarm` through `Deref`
and `DerefMut` instead of a method call is an unnecessary complication,
especially for newcomers. In addition, `Swarm` is not a smart-pointer
and should thus not make use of `Deref` and `DerefMut`, see documentation
from the standard library below.
> Deref should only be implemented for smart pointers to avoid
confusion.
https://doc.rust-lang.org/std/ops/trait.Deref.html
This commit implements the [libp2p circuit
relay](https://github.com/libp2p/specs/tree/master/relay) specification. It is
based on previous work from https://github.com/libp2p/rust-libp2p/pull/1134.
Instead of altering the `Transport` trait, the approach taken in this commit
is to wrap an existing implementation of `Transport` allowing one to:
- Intercept `dial` requests with a relayed address.
- Inject incoming relayed connections with the local node being the destination.
- Intercept `listen_on` requests pointing to a relay, ensuring to keep a
constant connection to the relay, waiting for incoming requests with the local
node being the destination.
More concretely one would wrap an existing `Transport` implementation as seen
below, allowing the `Relay` behaviour and the `RelayTransport` to communicate
via channels.
### Example
```rust
let (relay_transport, relay_behaviour) = new_transport_and_behaviour(
RelayConfig::default(),
MemoryTransport::default(),
);
let transport = relay_transport
.upgrade(upgrade::Version::V1)
.authenticate(plaintext)
.multiplex(YamuxConfig::default())
.boxed();
let mut swarm = Swarm::new(transport, relay_behaviour, local_peer_id);
let relay_addr = Multiaddr::from_str("/memory/1234").unwrap()
.with(Protocol::P2p(PeerId::random().into()))
.with(Protocol::P2pCircuit);
let dst_addr = relay_addr.clone().with(Protocol::Memory(5678));
// Listen for incoming connections via relay node (1234).
Swarm::listen_on(&mut swarm, relay_addr).unwrap();
// Dial node (5678) via relay node (1234).
Swarm::dial_addr(&mut swarm, dst_addr).unwrap();
```
Co-authored-by: Pierre Krieger <pierre.krieger1708@gmail.com>
Co-authored-by: Roman Borschel <romanb@users.noreply.github.com>
Co-authored-by: David Craven <david@craven.ch>
